Photosynthesis:

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Transcript of Photosynthesis:

Photosynthesis: An OverviewLight-Dependent ReactionAnatomy of a Leaf**About half a million chloroplasts in a chunk of leaf with a top surface area of 1 mm2. A typical mesophyll cell contains about 30-40 chloroplasts.ChloroplastsCarbon dioxide enters the leaf and oxygen exits by way of microscopic pores called stomata (from the Greek meaning “mouth”).StomataWater is absorbed by the roots and delivered to the leaves in veins. Leaves also use veins to export sugar to roots and other nonphotosynthetic parts of the plant. VeinsChloroplasts have two membranes surrounding a dense fluid called the stroma. StromaWithin the stroma is a third membrane system, made up of sacs called thylakoids. Thylakoid sacs can be stacked into columns called grana (singular, granum). Thylakoids house chlorophyll pigments, which absorb light energy.ThylakoidsThe thylakoid is where photosynthesis takes place because this is where the chlorophyll is located. It is the light energy that is abosrbed by chlorophyll that drives the process of photosynthesis and it is what gives plants their characteristic green color. ChlorophyllWhat is energy?Types of EnergyLightHeatElectricalSoundChemicalADP = Adenosine DiphosphateATP = Adenonsine TriphosphateThe Process of PhotosynthesisEndothermic ReactionPhotosynthesis is an endothermic reaction. This process absorbs light energy in order to break the bonds between the carbon dioxide molecule and water molecule. The absorbed solar energy is greater than the energy released then the new bonds are created in the glucose and oxygen molecules. Two Types of Reactions within PhotosynthesisLight-Dependent Reactions: These reactions require light energy in order for them to work. This is the first step in photosynthesis.

Light-Independent Reactions:

These reactions do NOT require energy in order to work. Chemical Energy: ATP & ADPWhere do these reactions take place?Thylakoid Role of WaterWater is required in this reaction as a source of electrons and hydrogen ions.

Enzymes on the inner surface of the thylakoid break up each water molecule into 2 electrons, 2 hydrogen ions and 1 oxygen atom.

These electrons replace the ones that were lost to the electron-transport chain.What happens when solar energy is absorbed? Chlorophyll absorbs sunlight and gives off high-energy electrons, which are passed to a series of electron carriers embedded in the thylakoid membrane. This is the first step in the process of photosynthesis. Hydrogen ions, some left behind by splitting of water and some pumped in from stroma build up a negative space in the stroma relative to the positive space in the thylakoid. As the hydrogen ions leave the thylakoid, they spin this protein channel called ATP synthase. This makes ADP bind with a phosphate group to make ATP!Role of Hydrogen IonsEnergy Conversions in PhotosynthesisThe process of photosynthesis involves 3 energy conversions:1) absorption of light energy2) conversion of light energy into chemical energy 3) storage of chemical energy in the form of sugars

Factors Affecting PhotosynthesisLight IntensityTemperatureCarbon Dioxide LevelsWaterThe ATP produced in the light-dependent reactions drive the Calvin Cycle. The part of photosynthesis, which takes place in the stroma, uses carbon dioxide gas to make more stable energy compounds like glucose. The Calvin Cycle: Light Independent Reaction